
UK Biobank (UKBB): This database contains only CMR data and is used for pre-training the CMR segmentation model (see Section REF ). In this work, we use a cohort of 700 healthy subjects, where the LV endocardial and epicardial borders and the RV endocardial border were manually traced at end diastole (ED) and end systole (ES) frames using the cvi42 software (version 5.1.1, Circle Cardiovascular Imaging Inc., Calgary, Alberta, Canada). CMR imaging was performed using a 1.5 T Siemens MAGNETOM Aera (see [1]} for further details of the image acquisition protocol).

EchoNet-Dynamic [2]}: This database contains only echocardiography data and is used for pre-training the echocardiography segmentation model (see Section REF ). Apical-4-chamber echocardiography images were acquired by skilled sonographers using iE33, Sonos, Acuson SC2000, Epiq 5G, or Epiq 7C ultrasound machines in a cohort of 10,030 patients. For all subjects, the endocardial borders was manually traced at ED and ES frames. For further details of the image acquisition protocol see [2]}.

Guy’s and St Thomas’ NHS Foundation Trust (GSTFT): This database contains paired CMR and echocardiography data for a cohort of 50 HF patients and a cohort of 50 CRT patients. The GSTFT HF database was used to train and validate the CMR and echocardiography segmentation models (see Section REF ). The GSTFT CRT database was used to train and validate the MMDL algorithm. Both studies were approved by the London Research Ethics Committee (11/LO/1232), all patients provided written informed consent for participation in this study and the research was conducted to the Helsinki Declaration guidelines on human research. CMR imaging was carried out on multiple scanners: Siemens Aera 1.5T, Siemens Biograph mMR 3T, Philips 1.5T Ingenia and Philips 1.5T and 3T Achieva. In this study, the cine CMR 4 chamber single-slice long-axis (la4Ch) data were used, which had a slice thickness between 6 and 10 mm and an in-plane resolution between 0.92x0.92mm2 and 2.4×2.4mm2. For the GSTFT CRT cohort, 2D echocardiography imaging was acquired prior to CRT and at 6-months follow-up. For both cohorts, the ultrasound machines used were Philips IE33 and EPIQ 7C (Phillips Medical Systems, Andover, MA, USA) and the General Electric Vivid E9 (GE Health Medical, Horten, Norway), each equipped with a matrix array transducer. In this study, the apical 4Ch view was used for the development and evaluation of the MMDL model, and the apical 2Ch and 4Ch views were employed to estimate the left ventricular end-diastolic volume (EDV), end-systolic volume (ESV) and LVEF at 6-months follow-up for the GSTFT CRT cohort. The echocardiography images had an in-plane resolution between 0.26x0.26mm2 and 0.62×0.62mm2.

